Specifically the invention includes an assembly combination and methodology for monitoring the thermal profile of an interior panel of a shut cabinet, for example, a power distribution box.
There are important applications in electrical power distribution that involve measurement of hot spots within electrical high voltage cabinets without compromising the safety of working personnel. One way is to open the cabinet door and make a quick thermal image of electrical panel. However, for a high voltage electrical cabinet, the door of the cabinet can only be opened if the power is first shut-off. As a safety precaution, the cabinet door is interlocked with the incoming power circuit breaker. The fact the power is turned off results in a cooling of electrical circuit breakers. This can result in the rapid redistribution of accumulated heat, precluding the identifications of the true hot spots. Also shutting off the power may not be desirable to the operation of down stream users.
An alternative, albeit expensive, method employed today involves installing one or more infrared transmitting windows in the cabinet door. This allows the direct thermal xe2x80x9cviewingxe2x80x9d of the interior of an electrical panel, without opening the cabinet door. The diameter of these windows is large in order to accommodate the large aperture of a thermal imaging camera""s objective lens. The typical window diameter is 3xe2x80x3 (75 mm). To maintain the NEMA (National Electrical Manufacturing Association) safety rating, such as 1, 2, 3, 4, or 12, of the cabinet, qualified personnel should perform the installation of this window(s); or they should be installed at the time the electrical cabinet is assembled. This involves the customization of the electrical cabinet. It is to these problems that the present invention is directed.
It is therefore a primary object of the present invention to provide a method and means for evaluating the thermal profile of the interior of an enclosure without degrading the integrity of the enclosure.
It is still another object of the present invention to provide a method and means for evaluating the thermal profile of the interior of the enclosure without opening any access door.
It is yet another object of the present invention to expand the breadth of applications for thermal imaging equipment by facilitating their use with enclosures containing heat generating equipment which needs to be monitored.
Still another object is to provide a means and method for surveying a broad internal area of an enclosure, again without violating the integrity thereof or accessing the interior through the opening of an enclosure door.
A still further object is to provide a means and method for making accurate thermal profiles of the interior of an enclosure even though the heat source within the enclosure may be positioned at various depths from the evaluating means.
These and other objects are obtained with the thermal imaging combination and method of the present invention. It occurred to the applicant that an innovative lens assembly design (designated a xe2x80x9cfisheyexe2x80x9d assembly by the applicant) could simplify this costly and difficult measurement. Rather than placing a large diameter window(s) in the face of the cabinet door, a ⅝xe2x80x3 (16 mm) hole is drilled in the center of the cabinet door. A ⅝xe2x80x3 hole is permitted without compromising the safety issues. The hole can be effectively sealed while not in use. As such, the door is still able to maintain its NEMA rating. The fisheye lens assembly with a 66xc2x0 diagonally wide angle field of view, can image a broad section of the cabinet interior for hot spots through this hole, in one exercise. The small objective lens of the fisheye assembly provides very wide angle viewing, at different depths, without compromising the quality of the received thermal image and the NEDT (Noise Equivalent Differential temperature) of the thermal imaging system.
In the preferred embodiment the design of the fisheye lens assembly includes multi-element, infrared transmitting optical material consistent with the spectral transmission characteristics of the thermal imager camera, for example, Model #s 7102, 7200 and 7515, manufactured by Mikron Instrument Company, Inc. of Oakland, N.J., (hereinafter xe2x80x9cMikronxe2x80x9d), connected to the fisheye assembly. The lenses are placed inside a precision housing with appropriate spacing between the various lenses. A mechanism for manual focusing allows the best image quality for various depths of field, typically between 4xe2x80x3 to 45xe2x80x3 distance. Therefore the user has the advantage of expanding the capabilities of the thermal imager, to cover practically all preventative maintenance applications.